Aluminum (7075, 6061, 5005, and/or 5052) is the currently recommended material for the chassis and rails in the CubeSat specification. However, it is unclear why other high performing materials, such as Titanium, are not among this list.

What is the rationale?

It is understood that complete disintegration during reenty is a primary consideration during material selection. This depends on Melting Temperature, and the Specific Heat of Ablation, but the total mass of a given material type clearly plays a role.

However, the chassis is only a small proportion of the 1.33kg mass limit of 1U CubeSats - which appears to be well within the allowable mass for a wider range of materials.

So why is the CubeSat specification so restrictive?